One type of power converter that has been of increasing interest is the inductor capacitor converter (“LLC converter”). In standard LLC converters the primary side current is the sum of the reflected secondary side current (divided by the turn ratio) and the magnetizing current.
FIG. 1 is a prior art circuit configuration of a common LLC converter 1 having a half-bridge structure. The LLC converter 1 represents a circuit composed by two inductors and a capacitor. A half-bridge circuit 3 is formed by a pair of power switches 5 and 7 for driving a resonant network 9. The LLC has three resonant parameters. A first resonant parameter is a series resonant inductor Lr, a second parameter is a series resonant capacitor Cr and a third resonant parameter is a magnetizing inductor Lm of a transformer 11.
The input terminal 13 of the LLC converter is a DC voltage. The transformer 11 isolates the half-bridge circuit 3 and the resonant network 9 from a rectification circuit 15 by a primary side winding 17 and two series secondary sides winding 19, 21. The two series secondary sides winding 19, 21 are coupled in series.
The rectification circuit 15 includes a pair of rectification diodes 23 and 25. The diodes 23 and 25 are connected to an output capacitor 27. The cathodes of the diodes 23, 25 are connected to the positive terminal of capacitor 27. The anode of diode 23 is connected to the positive terminal of the secondary side coil 19, and the anode of diode 25 is connected to the negative terminal of the secondary side coil 21. A common connection node between the coils 19, 21 is ground of an output voltage.
The power switches 5, 7 of the LLC converter 1 operate under the condition of equal pulse width, in general in the condition of 50%, minus a delay time. An adjustment of the output voltage is obtained by changing the operation frequency of the power switches 5, 7.
To provide proper driving signals for a LLC converter to stabilize the output current a current sense transformer can be used according to the state of the art. The current sense transformer is connected anti-parallel to the secondary side coils. One of the disadvantages of such a current sense transformer is that such current sense transformers are expensive, since they have to withstand a high isolation voltage of e.g. 4 kV. Furthermore, an additional overvoltage protection is needed on the output side because the LLC converter is current controlled only with the help of the current sense transformer. Such an overvoltage protection can for example be provided by an optocoupler and a zener diode, or a crowbar system. In combination with the current sense transformer, the use of an optocoupler and a zener diode makes the overall system quite expensive.
Therefore, better technique is demanded to solve the above problems to provide proper driving signals for LLC converters. A general object of the present disclosure is therefore to provide an alternative for providing proper driving signals for LLC converters that allows a cheaper sensing of the secondary side current and the secondary side voltage.